Metering pump having a tubular seal for sealing a main liquid from an auxiliary liquid

ABSTRACT

A metering pump includes a motor compartment with a drive compartment defining a drive chamber. The drive chamber has an inlet and an outlet for a main liquid. A drive piston is moveably arranged in reciprocating translational motion in the drive chamber. A controller for controlling the movement of the drive piston under the action of the main liquid. A metering compartment defines a metering chamber. The metering chamber has an inlet and an outlet for an auxiliary liquid. The outlet for the metering chamber is separated from the outlet of the driving chamber. A metering piston is arranged in the metering chamber. The metering piston is driven by the drive piston. A frustoconical sealing member is arranged with its small base facing the drive compartment. An extension of the metering piston has a diameter smaller than a body of the metering piston. The extension and the frustoconical sealing member form a suction valve. A suction-delivery portion is arranged on the metering piston. An extendable tubular element has a first end sealingly fastened to a tubular part that is fixed to the drive chamber. The metering chamber is connected to the drive chamber via the tubular part. A second end of the extendable tubular element is sealingly fastened to the metering piston, wherein a flow of the auxiliary liquid supplied by the metering compartment is substantially proportional to a flow of the main liquid.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a 371 of PCT/FR97/00380 filed on Mar. 4, 1997.

FIELD OF THE INVENTION

The invention relates to improvements to metering pumps of the typecomprising:

a drive compartment comprising a drive piston movable in reciprocatingtranslational motion in a drive chamber having an inlet and an outletfor main liquid, and means for controlling the movements of the pistonunder the action of the main liquid,

a metering compartment comprising a metering piston in a meteringchamber connected to the drive chamber and having an inlet for auxiliaryliquid, the metering piston being driven in reciprocating translationalmotion by the drive piston and being equipped with suction/deliverymeans,

the assembly being such that the flow of auxiliary liquid supplied bythe metering compartment is proportional or substantially proportionalto the flow of main liquid.

BACKGROUND OF THE INVENTION

Metering pumps of this type are known, particularly from EP-A-0,255,791or from FR-B-2,707,350. These pumps are especially useful for injectingan additive, consisting of the auxiliary liquid, into the main liquidwhich serves at the same time as drive fluid. Such metering pumps havemany uses. They make it possible, for example, to carry out a meteringof chlorine (auxiliary liquid) into water (main liquid) or a metering ofa drug for cattle into the water of a drinking trough or else to preparebeverages based on water (main liquid) and concentrate (fruit juiceconcentrate or tea concentrate) forming the auxiliary liquid.

For some uses, such as the metering of chlorine into water or of drugsfor cattle into water, the proportion of auxiliary product to be addedto the main liquid is low; it is relatively difficult to maintain thisproportion exactly, particularly on account of leaks, albeit veryslights, when a conventional seal is used, through which a rod slides,for example a connecting rod between the drive piston and the meteringpiston; such a seal does not make it possible to prevent tiny quantitiesof liquid on either side of the seal from being carried along due tocapillary action.

Metering accuracy is therefore impaired by these, albeit very small,leaks.

In addition to the metering inaccuracy, these leaks eventually lead tovarious other problems, for example to scale being deposited on the rod,when chlorine is metered into hard water, or to the growth of bacteria,when a sweetened concentrated beverage (auxiliary liquid) is meteredinto water (main liquid).

These problems only become more serious during operation, since frictioncauses irreparable wear of the seal, which is accompanied by an increasein the passage of liquid on either side of the seal.

SUMMARY OF THE INVENTION

The object of the invention is, to provide a metering pump of the typedefined above, which no longer has the abovementioned disadvantages.

According to the invention, a metering pump of the type defined above,in which the metering chamber comprises its own outlet orifice separatedfrom that of the drive chamber, is characterized in that the meteringchamber is isolated from the drive chamber by an extendable tubularelement, one end of which is sealingly fastened to a part fixed to thedrive chamber and the other end of which is sealingly fastened to themetering piston.

Preferably, the extendable tubular element is produced from a materialsuitable for withstanding the variations in pressure of the auxiliaryliquid and main liquid in the metering and drive chambers, so as toprevent any variation in the volume of the metering chamber other thanthat attributable to the displacement of the metering piston. Meteringaccuracy is thus ensured.

Such material for the tubular element consists especially of a suitableplastic, in particular polypropylene.

The extendable tubular element is advantageously formed by a kind ofsheath, of which the end fastened to the drive chamber comprises anouter peripheral bead sealingly clamped between a bearing surface of atubular part fixed to the drive chamber and a clamping element fastenedto this part, especially by screwing. The other end of the sheathcomprises an inner radial collar, through which passes a central hole,this collar being blocked against the metering piston by clampingbetween one end of this metering piston and a bearing element fixed to adriving rod of the drive piston, the rod comprising a threaded end whichpasses through the washer and which is screwed into the metering piston.

The sheath extendability which ensures sealing is advantageouslyobtained by means of folds on the cylindrical part of this sheath, so asto bring about longitudinal extendability as a result of the opening ofthe folds.

The longitudinal section of the sheath is zigzag-shaped, and the peaksof the zigzag are designed to form hinges for easy opening and closing,the faces of the sheath which extend between two peaks of the zigzag aresufficiently rigid to avoid being deformed under pressure.Advantageously, in the case of a sheath produced in one piece from thesame material, the peaks of the zigzag have a smaller thickness than thefaces.

BRIEF DESCRIPTION OF THE DRAWINGS

Apart from the arrangements explained above, the invention consists ofsome other arrangements which will be discussed more explicitly belowwith regard to particular exemplary embodiments which are described withreference to the accompanying drawings, but which are in no way limitingand in which;

FIG. 1 is a diagrammatic vertical axial section through a metering pumpaccording to the invention.

FIG. 2 is a partial diagrammatic vertical section through an alternativeembodiment of the metering device of FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIG. 1 of the drawings, a metering pump P, or proportionalmetering device, can be seen, comprising a drive compartment 1 with apiston 2 movable in reciprocating translational motion in a drivechamber 3. In the example illustrated, the piston 2 is of thedifferential type, but it could be of another type. The chamber 3comprises an inlet orifice 4 and an outlet orifice 5 for main liquid.The chamber 3 is closed in the upper part by means of a cap not shown.

Distribution means D are provided for controlling the reciprocatingmovements of the piston under the action of the main liquid entering viathe orifice 4. These distribution means D, known, for example, fromEP-A-0,255,791 or FR-B-2,707,350, are shown only highly diagrammaticallyand will not be described in detail. It is merely recalled that thesemeans D may tilt from a first to a second position and vice versa. Themeans D make it possible, in the first position, to displace the piston2 in the direction moving it away from the inlet orifice 4, with mainliquid being admitted into the chamber 1, and, in the second position,to displace the piston 2 in the opposite direction, with a specificvolume of main liquid being delivered via the outlet orifice 5. Thereversal of the distribution means D is controlled mechanically at theend of each outward or return stroke of the piston 2.

The metering pump P also comprises a metering compartment 6 with ametering piston 7 movable in reciprocating translational motion in ametering chamber 8 coaxial to the drive chamber 1.

The metering chamber 8 is delimited by a cylindrical wall 9 provided, atits lower end, with a nipple 10, to which a pipe 11 for the suction ofthe auxiliary product is connected. The pipe 11 is submerged with itslower end, not shown, in a receptacle containing the auxiliary liquid. Asuction valve 12 is mounted in the nipple 10. The valve 12 is designedto open when the metering piston 7 moves away from the nipple 10 andsucks in liquid, while the valve 12 closes when the piston 7 approachesthe nipple 10.

The cylindrical wall 9 is fastened coaxially to a tubular part 13 openat its two axial ends, this part 13 being fixed to the drive chamber 3.The part 13 forms a kind of cylindrical sleeve comprising on its outerwall, in the upper part, a shoulder 14 which comes into axial abutmentagainst the upper end of a seat 15 provided in the bottom of the chamber3. The part 13 can be blocked in terms of axial translational motion onthe seat 15 by means of a screw 16 which is oriented transversely to theaxis of the seat 15 and the inner end of which is engaged in a recessprovided on the surface of the part 13.

The lower end of the part 13 projects beyond the base of the chamber 3and is preferably provided with a thread 17 on its outer surface. Thewall 9 is provided with a thread 18 in the upper part of its outersurface. The wall 9 and the part 13 are assembled with the aid of aninternally threaded intermediate sleeve 19; the inner volume of thecylindrical wall 9 communicates with the inner space of the part 13.

The metering piston 7 comprises a head 20, the outside diameter of whichis equal to the diameter of the bore of the wall 9, and a piston body 21of smaller diameter, extending from the head 20 toward the drive chamber3. The head 20 is equipped with a suction/delivery means 22. This means22 includes of an annular seal, for example of square section, arrangedin a peripheral groove of the head 20.

The piston 7 comprises a recess 23 extending parallel to its axialdirection from the groove, in which the seal/valve 22 is accommodated,on the opposite side to the suction valve 12. This recess 23 has anangular extent sufficient to impart some freedom of movement to thatpart of the seal 22 which is located in the recess 23.

Under these conditions, when the piston 7 is displaced upward accordingto the figure, the seal 22 is laid against the lower transverse face ofthe groove forming its receptacle and maintains sealing between the twospaces located on either side of the head 20. Auxiliary liquid is suckedinto the lower space located below the head 20, in the chamber 8. Bycontrast, during the descending movement of the piston 20, when thevalve 12 has closed, the seal 22 in the part of the recess 23 will riseand allow auxiliary liquid to pass from the lower space to the spacelocated above the head 20 of the piston 7.

The metering chamber 8 has its own outlet orifice 24 separated from theoutlet orifice 5 of the drive chamber. If the auxiliary liquid is anadditive product to be mixed with the main liquid, mixing may take placedownstream of the pump P by joining together the conduits connectedrespectively to the orifices 5 and 24.

The body 21 of the piston 7 is connected by a rod 25 to the differentialdrive piston 2 which controls the displacements of the metering piston7. The lower end 26 of the rod 25 is threaded and is screwed into acoaxial internally threaded hole in the upper end of the piston body 21.

The metering chamber 8 is isolated from the drive chamber 3 byfull-sealing sealing means E which comprise an extendable tubularelement T, one end 27 of which, namely the upper end according to thedrawing, is sealingly fastened to the part 13 fixed to the drive chamber3 and the other end 28 of which is sealingly fastened to the meteringpiston 7.

The extendable tubular element T advantageously comprises an extendablesheath 29 produced from a material sufficiently rigid to withstand theexternal or internal hydraulic pressure. The extendability of the sheath29 is obtained by folding the cylindrical part of this sheath, so as toproduce a zigzag-shaped profile capable of being unfolded longitudinallyin the direction of the axis of the tube T by virtue of the hinges orjoints formed by the peaks 29a of the profile. However, the material ofthe sheath is sufficiently rigid to ensure that those faces 29b of thefolds which are contained between two peaks 29a are not appreciablydeformed under the effect of the hydraulic pressure. Metering istherefore not impaired by variations in volume of the metering chamber 8other than those attributable to the displacement of the piston 7.

As regards a sheath 29 produced in one piece from the same material, thejoint flexibility of the peaks 29a may be obtained by means of a smallerthickness than that of the faces 29b.

The sheath 29 is preferably produced from a plastic, in particularpolypropylene.

The upper end 27 of the sheath 29 forms an outer bead 30 clamped in anannular receptacle of the part 13, against a shoulder of this part, by acap 31 having a central aperture for the passage of the rod 25, with awasher being interposed. The cap 31 is provided externally with acylindrical rim having an internal thread capable of being screwed ontoan external thread of the upper end of the part 13. The lower end 28 ofthe sheath 29 includes a collar projecting radially inward and providedwith a central hole for the passage of the end 26 of the rod 25. Thiscollar is sealingly clamped between the transverse end of the body 21 ofthe piston 7 and a disk 32 fixed to the rod 25.

The assembly is designed in such a way that the stroke of the head 20 ofthe piston 7 takes place solely within the bore of the cylindrical wall9.

This being so, the metering pump functions as follows.

The reciprocating translational movements of the differential drivepiston 2 are transmitted to the metering piston 7 by the rod 25.

When this piston 7 executes an ascending stroke (according to thedrawing), auxiliary liquid from the chamber 8 is delivered via theoutlet 24, while auxiliary liquid coming from the pipe 11 is suckedthrough the valve 12 into the space located below the head 20.

During the descent of the piston 7, as explained above, the seal/valve22 executes a movement allowing auxiliary liquid to pass from the spacelocated under the piston head 20 to the space located above this head,when the valve 12 is closed.

The extendable tubular element T ensures full sealing, in such a waythat the problems mentioned above, such as scale being deposited on therod 25, when chlorine is metered into hard water, or the growth ofbacteria, when the main liquid is water and the auxiliary liquid is asweetened concentrated beverage, no longer exist.

Metering accuracy is ensured, in particular, as a result of thesufficient rigidity of the material forming the folded sheath T andwithstanding the hydraulic pressure.

There is no longer any friction between the extendable tubular sealingelement T and the connecting rod 25.

Referring to FIG. 2 of the drawings, an alternative embodiment of themetering pump according to the invention can be seen. Elements of thisalternative which are similar to elements already described with regardto FIG. 1 or perform the same functions are designated by referencenumerals equal to the sum of the number 100 and the reference numberused in FIG. 1. The description of these elements will not be repeatedor will be given only briefly.

The cylindrical wall 109 and the tubular part 113 form one part whichmust be engaged from above (according to the illustration in FIG. 2)through the orifice delimited by the seat 115, against which a shoulder114 of the part 113 comes to bear axially. This part 113 comprises, on aregion of its outer surface located below the seat 115 when the assemblyis in place, a thread, onto which can be screwed a nut 33 which makes itpossible to block all the parts 109 and 113 on the drive chamber 103.

The metering piston 107 has a head 120 of a diameter slightly greaterthan that of the body 121. The relative difference between the diameterof this head and that of the body 121 is less marked than in the exampleof FIG. 1.

The metering piston 107 comprises, at its end remote from the drivecompartment 101, an extension 34 of smaller diameter than the body 121.This coaxial extension 34 passes through a flexible frustoconicalsealing member 35 in order to penetrate into a cylindrical space 36having a diameter greater than that of the extension 34. This space 36is located in the nipple 110. The axial length of the extension 34 isgreater than the stroke of the piston 107, so that the extension 34always passes through the frustoconical member 35. The small base ofthis sealing member 35, produced, for example, from elastomericmaterial, faces the drive compartment 101, while its large basecomprises a collar projecting radially outward and clamped between ashoulder of the cylindrical wall 109 and another shoulder of the nipple110.

When the piston 107 rises according to FIG. 2, the frustoconical member35 tends to open and allow auxiliary liquid sucked in by the meteringpiston 107 and its extension 34 to pass. During the descent of thepiston 107, the frustoconical member 35 tends to be laid sealinglyagainst the extension 34 and prevents any flow of liquid from themetering chamber 108 toward the space 36.

The combination of the extension 34 and of the sealing member 35constitutes a suction means 112 equivalent to the valve 12 of FIG. 1.

The overall functioning of the metering pump of FIG. 2 is similar tothat described with regard to FIG. 1.

The use of an unrolling diaphragm instead of the folded tubular sheathwould make it possible to ensure sealing, but would present problems dueto the relatively long strokes of the metering pumps and would lead to ametering error because a diaphragm does not have sufficient rigidity towithstand the hydraulic pressure and is deformed in the manner of abladder.

A simple concertina made of elastomeric material and easy to produce byhardening would give rise to the same problems as the diaphragmmentioned above.

The solution of the unrolling diaphragm or of the concertina made ofelastomeric material may be appropriate if the only aim is sealing,without the further requirement of high metering accuracy.

What is claimed is:
 1. A metering pump comprising:a drive compartmentdefining a drive chamber, the drive chamber having an inlet and anoutlet for a main liquid; a drive piston moveably arranged inreciprocating translational motion in the drive chamber; distributionmeans controlling movement on the drive piston under action of the mainliquid; a metering compartment defining a metering chamber, the meteringchamber having an inlet and an outlet for an auxiliary liquid, theoutlet for the metering chamber being separated from the outlet of thedriving chamber; a metering piston arranged in the metering chamber, themetering piston being driven by the drive piston; a frustoconicalsealing member arranged with its small base facing the drivecompartment, an extension of the metering piston, having a diametersmaller than a body of the metering piston, passing through thefrustoconical sealing member, the extension and the frustoconicalsealing member forming a suction valve; suction-delivery means arrangedon the metering piston; and an extendable tubular element having a firstend sealingly fastened to a tubular part that is fixed to the drivechamber, the metering chamber being connected to the drive chamber viathe tubular part, a second end of the extendable tubular elementsealingly fastened to the metering piston, wherein a flow of theauxiliary liquid is supplied by the metering compartment substantiallyproportional to a flow of the main liquid.
 2. Metering pump according toclaim 1, wherein the extendable tubular element is formed from amaterial suitable for withstanding the variations in pressure of theauxiliary liquid and main liquid in the metering and drive chambers, soas to prevent any variation in the volume of the metering chamber otherthan that attributable to the displacement of the metering piston. 3.Metering pump according to claim 1, wherein the material of the tubularelement consists of a plastic.
 4. Metering pump according to claim 3,wherein the plastic is polypropylene.
 5. Metering pump according toclaim 1, wherein the extendable tubular element is formed by a sheath,an end of the sheath is fastened to the drive chamber and comprises anouter peripheral bead sealingly clamped between a bearing surface of thetubular part fixed to the drive chamber and a clamping element fastenedto the tubular part, a second end of the sheath comprises an innerradial collar, through which passes a central hole, the collar beingblocked against the metering piston by clamping between one end of themetering piston and a bearing element fixed to a driving rod of thedrive piston, the driving rod comprising a threaded end screwed into themetering piston.
 6. Metering pump according to claim 1, wherein theextendable tubular element comprises a sheath, the sheath having foldson its cylindrical part, longitudinal extendability of the sheath isprovided as a result of the opening of the folds.
 7. Metering pumpaccording to claim 6, wherein a longitudinal section of the sheath iszigzag-shaped, and peaks of the zigzag form hinges with easy opening andclosing, while faces of the sheath which extend between two peaks of thezigzag-shape are sufficiently rigid to avoid being deformed underpressure.
 8. Metering pump according to claim 7, wherein the sheath isproduced in one piece.
 9. Metering pump according to claim 8, whereinthe peaks of the zigzag have a smaller thickness than the faces.